Heretofore, as an electrophotographic photoreceptor, there has widely been used an inorganic photoreceptor, wherein a light-sensitive layer whose main component is an inorganic photoconductive material such as selenium, zinc oxide and cadmium sulfate is provided. However, the inorganic photoreceptor is not always satisfactory in terms of properties such as light sensitivity, heat stability, resistance to humidity and durability that are requested for an electrophotographic photoreceptor of a copying machine. In addition, electrophotographic photoreceptors containing selenium and cadmium sulfate have a shortcoming in that they have severe restriction in manufacturing and handling due to their toxicity.
In order to overcome the above-mentioned shortcomings, there have been developed recently, electrophotographic photoreceptors using various organic photoconductive materials. Especially, a function-separation type electrophotographic photoreceptor wherein a carrier-generation function and a carrier-transportation function are assigned to different materials separately, is advantageous for enhancement of performance because of the appropriate substances can be selected from a wide range. Accordingly, it is dominant among organic photoreceptors in use practically currently.
As a carrier-generation material and a carrier-transportation material of the above-mentioned function-separation type electrophotographic photoreceptor, various organic compounds have been proposed. As a carrier-generation material, so far, various photoconductive materials such as polycyclic quinone compounds represented by dibromoanthanthlone, pyrylium compounds and euteric complexes of pyrylium compounds, photoconductive materials such as squarelium compounds, phthalocyanine compounds and azo compounds have been put into practical use. In addition, with regard to perylene compounds, Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 54267/1987 (U.S. Pat. No. 4,714,666) and Japanese Patent O.P.I. Publication No. 6014/1993 (U.S. Pat. No. 5,019,473) disclose technologies to use these compounds as carrier-generation materials.
As stated above, several experiments have been carried out. However, demand for enhancement of sensitivity of an electrophotographic photoreceptor has been increasing recently. Under these circumstance, the above-mentioned conventional technologies have not been considered satisfactory.